Distributed antenna system

ABSTRACT

The present disclosure is a novel utility of a software defined radio (SDR) based Distributed Antenna System (DAS) that is field reconfigurable and support multi-modulation schemes (modulation-independent), multi-carriers, multi-frequency bands and multi-channels. The present invention enables a high degree of flexibility to manage, control, enhance, facilitate the usage and performance of a distributed wireless network such as Flexible Simulcast, automatic traffic load-balancing, network and radio resource optimization, network calibration, autonomous/assisted commissioning, carrier pooling, automatic frequency selection, frequency carrier placement, traffic monitoring, traffic tagging, pilot beacon, etc. As a result, a DAS in accordance with the present invention can increase the efficiency and traffic capacity of the operators&#39; wireless network.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/260,145, filed Apr. 23, 2014, which is a continuation ofU.S. patent application Ser. No. 13/211,247, filed Aug. 16, 2011, whichclaims the benefit of U.S. Provisional Patent Application No.61/439,940, filed Feb. 7, 2011, the disclosures of which are herebyincorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention generally relates to wireless communicationsystems employing Distributed Antenna Systems (DAS) as part of adistributed wireless network. More specifically, the present inventionrelates to a DAS utilizing one or more remotely monitored and controlleddigital access units configured to assign particular packettransmissions to selected ones of a plurality of remote units, which canin some embodiments be configured in a daisy-chained rings.

BACKGROUND OF THE INVENTION

Wireless and mobile network operators face the continuing challenge ofbuilding networks that effectively manage high data-traffic growthrates. Mobility and an increased level of multimedia content for endusers requires end-to-end network adaptations that support both newservices and the increased demand for broadband and flat-rate Internetaccess. One of the most difficult challenges faced by network operatorsis maximizing the capacity of their DAS networks while ensuringcost-effective DAS deployments and at the same time providing a veryhigh degree of DAS remote unit availability.

In order to provide DAS network capacity which is high enough to meetshort-term needs of network subscribers in specific locations yet alsoavoid costly and inefficient deployment of radio resources, DAS networkplanners prefer to employ DAS architectures and solutions which providea high degree of dynamic flexibility. Therefore, it would beadvantageous for wireless network operators to employ a DAS solutionwhich has a high degree of flexibility to implement dynamicrearrangements based on ever-changing network conditions and subscriberneeds. Also, the more future-proof a DAS deployment can be, generallythe lower its life cycle cost.

DAS network planners and system integrators employ a wide range ofinnovative approaches for helping to ensure that a particular DASdeployment is as cost-effective as possible. The types of costsconsidered by network planners and integrators include DAS deployment orDAS installation cost, as well as operational costs includingmaintenance costs, emergency restoration costs and networkre-arrangement costs. Rearrangement costs are particularly significantfor indoor DAS applications, due to frequent changes in building use andfacility needs changes. Therefore, it would be advantageous to employDAS systems and methods which are based on as few DAS transportfacilities as possible to minimize installation and/or lease costs andhave self-healing capabilities to avoid the need for costly emergencyrestoration services.

In order to obtain a high degree of DAS remote unit availability, twoprimary conditions must be satisfied. First, the DAS remote unit itselfmust be inherently reliable. Second, the transport media e.g., opticalfiber, must be very reliable. It is well known that electronic and/oroptical connections themselves are a significant root cause of failureor reduced availability in a DAS network. Companies who maintain outdoorDAS networks have reported that a failure of outside plant optical fiberfacilities is not as rare as would be desirable. Therefore, it would beadvantageous to employ systems and methods which offer higher redundancyand/or self-healing features in the event of failure of a transportmedia connection.

SUMMARY OF THE INVENTION

The present invention substantially achieves the advantages and benefitsdiscussed above and overcomes the limitations of the prior art discussedabove by providing a distributed antenna system responsive to one ormore base stations and having at least one but in some embodiments aplurality of Digital Access Units (“DAU's”), each operating to controlthe packet traffic of an associated plurality of Digital Remote Units(“DRU's”). In embodiments employing multiple DAU's, the DAU's can bedaisy-chained linearly or in a ring configuration. Likewise, dependingupon the implementation, the DRU's associated with a given DAU can beconfigured in either a linear or ring Daisy chain configuration.

The data received from the base stations is down-converted, digitizedand converted to baseband with the DAU. The data streams are then I/Qmapped and framed and independently serialized, such that multiple datastreams are available in parallel from the DAU. In at least someembodiments, the DAU communicates with the associated DRU's via anoptical transport arrangement. It will be appreciated by those skilledin the art that, using the present invention, it is possible toconfigure a distributed antenna system having n base stations, eachproviding m RF outputs for transmission by one or more associated DAU'sto o DRU's, where the only limits are imposed by the technicalperformance specifications of the particular DAS, such as delay.

By the use of a ring configuration for connecting, in at least someembodiments, the DRU's and/or the DAU's, fault tolerance is built intothe system, with resulting high availability. In single DAU embodiments,each DRU is accessible through two paths, and therefore remainsavailable even in the event of a line break. In multi-DAU embodiments,where the DAU's are linearly daisy-chained, each DRU is accessible frommultiple DRU's such that even some DAU failures will not prevent systemoperation. In embodiments employing a ring connection for the DAU's,multiple paths exist to each DAU, and thus provide an additional levelof fault tolerance as well as dynamic load balancing and resourcemanagement as discussed in greater detail hereinafter.

Thus, the configuration of the advanced system architecture of thepresent invention provides a high degree of flexibility to manage,control, enhance and facilitate the radio resource efficiency, usage,availability, and overall performance of the distributed wirelessnetwork. The present invention enables specialized applications andenhancements including Flexible Simulcast, automatic trafficload-balancing, network and radio resource optimization, networkcalibration, autonomous/assisted commissioning, carrier pooling,automatic frequency selection, radio frequency carrier placement,traffic monitoring, traffic tagging, and indoor location determinationusing pilot beacons. The present invention can also serve multipleoperators, multi-mode radios (modulation-independent) andmulti-frequency bands per operator to increase the efficiency andtraffic capacity of the operators' wireless networks.

Further the present invention provides a high degree of dynamicflexibility, supports dynamic re-arrangements, and provides a low lifecycle cost. This advanced system architecture enables deployment of DASnetworks using fewer DAS transport facilities to reduce costs, whileproviding self-healing features. The present invention also offersredundancy and enhanced system availability.

It is an object of the present invention to provide Flexible Simulcastcapabilities, as disclosed in U.S. Provisional Application Ser. No.61/382,836, entitled “Remotely Reconfigurable Distributed Antenna Systemand Methods,” filed Sep. 14, 2010, incorporated herein by reference, ina high-availability ring configuration using, for example, optical fibertransport. As discussed above, the ring configuration insures that abreak in any optical fiber cable will not shut down the daisy-chainednetwork, because the downlink and uplink signals can be rerouted aroundthe cable break to the respective DRUs.

It is a further object of the present invention to balance thebidirectional data rate on the optical fibers so as to increase themaximum achievable data rate during operation on the ring network ofDRUs.

It is a further object of the present invention to provide highertransport network capacity in the event the data transport isasymmetrical between the downlink and uplink, as is typically the casefor mobile broadband networks.

It is a further object of the present invention to provide an adaptiveand automatic control for optimizing the transport media capacity on thering.

It is a further object of the present invention to provide a method ofsumming co-channel users' uplink signals in the DRU daisy chain.

Applications of the present invention are suitable to be employed withdistributed base stations, distributed antenna systems, distributedrepeaters, mobile equipment and wireless terminals, portable wirelessdevices, and other wireless communication systems such as microwave andsatellite communications. The present invention is also field upgradablethrough a link such as an Ethernet connection to a remote computingcenter.

Appendix I is a glossary of terms used herein, including acronyms.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the present invention can be morefully understood from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram according to one embodiment of the inventionshowing the basic structure and an example of a unidirectional,channelized downlink transport, one ring scenario based on having oneDAU and four DRUs.

FIG. 2 is a block diagram in accordance with an embodiment of theinvention showing the basic structure and an example of aunidirectional, channelized uplink transport, one ring scenario based onhaving one DAU and four DRUs.

FIG. 3 is a block diagram in accordance with an embodiment of theinvention showing the basic structure and an example of aunidirectional, channelized uplink transport, two ring scenario based onhaving one DAU and eight DRUs.

FIG. 4 is a block diagram in accordance with an embodiment of theinvention showing the basic structure and an example of a unidirectionalchannelized uplink or downlink transport. This example of a five ringscenario comprises two DAUs and twenty DRUs. FIG. 4 provides an exampleof a daisy chain ring network.

FIG. 5 illustrates an embodiment of a cellular network system employingmultiple DRUs according to the present invention.

FIG. 6 illustrates an embodiment of a multi-band system employing sixdifferent services operating in different frequency channels withmultiple DRUs according to the present invention.

FIG. 7 illustrates in block diagram form the interaction between the DAUembedded software control module and the DRU embedded software controlmodule.

FIG. 8 illustrates in block diagram form an embodiment of a DASaccording to an aspect of the invention, including daisy-chained DAU's.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a novel Reconfigurable Distributed AntennaSystem that provides a high degree of flexibility to manage, control,re-configure, enhance and facilitate the radio resource efficiency,usage and overall performance of the distributed wireless network. FIG.1 illustrates an embodiment of the Distributed Antenna System 100 thatprovides an example of a unidirectional, channelized downlink transportin accordance with the present invention. In FIGS. 1-4, a dotted linedenotes a distinct subset of uplink and downlink channels identified as“A.” A dashed line denotes a distinct subset of uplink and downlinkchannels identified as “B.” The subset of uplink and downlink channelsin A do not include those of B and vice versa. The system employs aDigital Access Unit functionality 105 (hereinafter “DAU”). The DAU 105serves as an interface between associated base stations (BTS) 110A-B anda plurality of digital remote units (DRU) 125A-n, although only fourDRU's are shown in FIG. 1. In the present description, “DRU” will beused interchangeably with Remote Radio Head Unit, or “RRU”, because ofthe similarity of the functions discussed herein, although those skilledin the art will recognize that a DRU communicates with a DAU, whereas anRRU communicates with a base station. In addition, those skilled in theart will recognize that a DAU is monitored and controlled by a remotenetwork operations center (“NOC”), as indicated at bidirectional link115 in FIG. 1. Such links are typically Ethernet connections or externalmodems, but can be any form of link suitable for remote monitoring andcontrol. The NOC has the capability to remotely configure the DAUparameter settings which in turn configures the DRU's parametersettings. The NOC can request information from the DAUs. The DAUs cansubsequently request information from the DRUs. The informationrequested includes but is not limited to uplink power, downlink power,optical error rate, gain settings, active carriers, etc.

For the downlink (DL) path, RF input signals 120A through 120 n arereceived at the DAU 105 from one or more base station units (BTS)indicated at 110A through 11 Op. The RF input signals are separatelydown-converted, digitized, and converted to baseband (using a DigitalDown-Converter) by the DAU. Data streams are then I/Q mapped and framedand specific parallel data streams are then independently serialized andtranslated to optical signals using pluggable SFP modules, again by theDAU 105. The independently serialized, parallel data streams are thendelivered to different DRU's 125A-125 k, typically over optical fibercable arranged, in at least some embodiments, in a ring configurationindicated at connection pairs 140A-145A, or, in other embodiments, adaisy chain configuration. In addition, each DAU can support a pluralityof rings with associated DRU's, where the additional rings are indicatedby fiber optic pairs up through 140 o-145 o. It will be appreciated bythose skilled in the art that the number of RF inputs, DAU's and DRU'sand rings is limited only by network performance factors, such as delay.In addition, as discussed in connection with FIG. 4 herein, the DAS canbe further extended by using a ring or daisy-chain of DAU's, each ofwhich supports an arrangement of DRU's and rings as shown in FIG. 1.

One function of the DAU 105 is to determine the direction in whichdownlinked channels are propagated around the ring. As just one example,the embodiment shown in FIG. 1 is configured to have downlink channelsA, B, C and D propagate in a first direction, for example clockwise, andchannels E, F, G, and H propagate in the counter direction, although itwill be understood that the number of channels propagating in eachdirection need not be equal, nor adjacent, nor sequential. Likewise, thenumber of channels received at each DRU is assigned by the DAU and neednot be equal, adjacent or sequential, but instead will typically be anyconfiguration that optimizes network utilization.

Referring next to FIG. 2, an embodiment of an uplink (UL) path inaccordance with the invention can be better appreciated. Channelsreceived at the antenna associated with each DRU are converted intooptical signals by each DRU 125A-125 k. Optical signals received fromthe DRU's are de-serialized and de-framed by the DAU 105, and are alsoup-converted digitally using a Digital Up-Converter implemented withinthe DAU 105. Each data stream is then independently converted to theanalog domain and up-converted to the appropriate RF frequency band,still within the DAU 105 in the illustrated implementation, althoughthis functionality can be separate. The RF signals are then delivered tothe appropriate one of a plurality of BTS' 110A-110 p. As with thearrangement shown in FIG. 1, the direction of propagation of eachchannel is controlled by the DAU, with some channels propagating in aclockwise direction and others in a counterclockwise direction. Also asdiscussed in connection with FIG. 1, while adjacent channels are shownas propagating in the same direction in FIG. 2, this is not required andany channel can be selected to propagate in either direction.

Referring again to FIG. 1, it will be appreciated by those skilled inthe art that, in some implementations of a DAS, more than one carriercan exist in each channel, and, as such, a DRU may receive a channelcomprising a signal containing two or more carriers, or a wirelessoperator may have more than one RF carrier per channel allocated to asingle base station. This is referred to as a “composite signal”. Themanner in which a composite downlink signal is managed by the presentinvention can be better understood with reference to FIG. 1. In suchinstances, the DAU will receive a composite downlink input signal 130from, e.g., a first base station 110A belonging to one wirelessoperator, enters the DAU 105 at the RF input port 120A. Composite signal130 comprises carriers A-D. A second composite downlink input signalfrom e.g., a pth base station 110 p belonging to the same wirelessoperator enters DAM at the DAU1 RF input port 120 n. Composite signal135 comprises carriers E-H. The functionality of the DAU 105, and DRU's125A-125 k, respectively, are explained in detail in U.S. ProvisionalApplication Ser. No. 61/374,593, entitled “Neutral Host Architecture fora Distributed Antenna System,” filed Aug. 17, 2010, the disclosure ofwhich is hereby incorporated by reference in its entirety for allpurposes.

One optical output of DAU 105 is fed to DRU 125A, via bidirectionaloptical cable 140A. A second optical output of DAU 105 is fed viabidirectional optical cable 145A to DRU3. Similarly, bidirectionaloptical cables 150, 155 and 160 connect DRU's 125A-n in a ringconfiguration, such that DRU 125A connects to DRU 125B via cable 150A,DRU 125B connects to DRU 125 n via cable 15013, and DRU 125 k connectsto DRU 125C, or the kth-1 DRU, via cable 150 m. This connectionfacilitates networking of DAU 105, which means that all of Carriers A-Hare available within DAU 105 to transport data to DRU's 125A-k dependingon software settings within the networked DAU system. Depending upon theembodiment, the software settings within DRU 125A are configured eithermanually or automatically, such that carriers A-H are present in thedownlink output signal 155A at the antenna port of DRU 125A. Thepresence of all eight carriers means that DRU 125A is potentially ableto access the full capacity of both base stations feeding DAU 105. Apossible application for DRU 125A is a cafeteria in an enterprisebuilding during the lunch hour where a large number of wirelesssubscribers are gathered.

DRU 125B is fed by a second optical port of DRU 125A via bidirectionaloptical cable 150A. The optical cable 150A performs the function ofdaisy chaining DRU 125A with DRU 12513. As with DRU 125A, the softwaresettings within DRU 125B are configured either manually or automaticallysuch that Carriers A, C, D and F are present in downlink output signal155E at the antenna port of DRU 1258. The capacity of DRU 125B is set toa much lower value than DRU 125A by virtue of its specific channelsettings as controlled by DAU 105. The individual Digital Remote Unitshave integrated frequency selective DUCs and DDCs with gain control foreach carrier. The DAU's can remotely turn on and off the individualcarriers via the gain control parameters.

In a similar manner as described previously for DRU 125A, the softwaresettings within DRU 125C are configured either manually or automaticallysuch that Carriers B and F are present in downlink output signal 155C atthe antenna port of DRU 125C. Compared to the downlink signal 155B atthe antenna port of DRU 12513, the capacity of DRU 125C, which is alsoconfigured via its software settings, is much less than the capacity ofDRU 125B. DRU 125 n is fed by the optical cable 150 m connected to thesecond optical port of the n^(th)−1 DRU, shown for simplicity in FIG. 1as DRU 125C. The software settings within DRU 125 n are configuredeither manually or automatically such that carriers A, D, E and H arepresent in downlink output signal 155D at the antenna port of DRU 125 n.Typically, the capacity of DRU 125 n is set to a much lower value thanDRU 125A, however, the relative capacity settings of each of DRU's125A-n can be adjusted dynamically to meet the capacity needs within thecoverage zones determined by the physical positions of antennasconnected to those DRU's. As noted above, the ring connection iscompleted by interconnecting DRU 125B and DRU 125 n through opticalcable 150B. The ring configuration insures that any optical cable breakswill not shut down the daisy chained network. The downlink and uplinksignals will be rerouted around the cable break to the respective DRUs.

The present invention facilitates conversion and transport of severaldiscrete relatively narrow RF bandwidths. This approach allowsconversion of only those multiple specific relatively narrow bandwidthswhich carry useful or specific information. This approach also allowsmore efficient use of the available optical fiber transport bandwidthfor neutral host applications, and allows transport of more individualoperators' band segments over the optical fiber. As disclosed in U.S.Provisional Application Ser. No. 61/374,593, entitled “Neutral HostArchitecture for a Distributed Antenna System,” filed Aug. 17, 2010together with U.S. Provisional Application Ser. No. 61/382,836, entitled“Remotely Reconfigurable Distributed Antenna System and Methods”, filedSep. 14, 2010, both assigned to the assignee of the present invention,and also referring to FIG. 1 of the instant patent application, DigitalUp Converters located within the DRU can be dynamically reconfigured asthe result of commands from the NOC to transport from the DAU input toany specific DRU output any specific narrow frequency band or bands, RFcarriers or RF channels which are available at the respective RF inputport of either DAU. This capability is illustrated in FIG. 1 where onlyspecific frequency bands or RF carriers appear at the output of a givenDRU. More specifically, through commands received from the NOC, theFPGA's in the DAU and one or more of the associated DRU's can bereprogrammed or reconfigured to convert and transport only the desirednarrow bandwidths.

A related capability of the present invention is that not only can theDigital Up Converters located within each DRU be configured to transportany specific narrow frequency band from the DAU input to any specificDRU output, but also the Digital Up Converters within each DRU can beconfigured to transport any specific time slot or time slots of eachcarrier from the DAU input to any specific DRU output. The carriers andtime slots are monitored by the DAU by filtering the signals andperforming power detection of the individual time slots, whichinformation can be conveyed to the NOC as desired. Then, as with theDigital Up Converters, the Field Programmable Gate Arrays (FPGA) in theDAU or DRU can be dynamically reconfigured by commands received from theNOC in a manner analogous to software programmability. The DAU detectswhich carriers and corresponding time slots are active. This informationis relayed to the individual DRUs via the management control andmonitoring protocol software. This information is then used, asappropriate, by the DRUs for turning off and on individual carriers andtheir corresponding time slots.

Data transport between the Base Station and the subscribers is typicallyasymmetrical, whereby the downlink data rate is higher than the uplinkrate. The ring network configuration of Daisy Chained DRUs can exploitthis data rate asymmetry to maximize the data transport on the opticalfibers 150A-150 m.

The present invention balances the bidirectional data rate on theoptical fibers so as to increase the maximum achievable data rate on thering network of DRUs. The individual downlink channels are transmittedin a unidirectional sense along the ring network. Referring to FIG. 1,downlink channels A, B, C, and D are transmitted in a clockwise sensearound the ring of DRU's 125A-k. On the other hand, downlink channels E,F, G and H are transmitted in a counterclockwise sense around the ringof DRUs. Referring to FIG. 2, the uplink channels J, K, L and M aretransmitted in a counterclockwise sense whereas uplink channels N, O, Pand Q are transmitted in a clockwise sense around the ring of DRUs. Ifthe downlink and uplink data rates were the same, there would be noadvantage in the transport mechanism. However, if the data transport isasymmetrical between the downlink and uplink then a significantadvantage can be gained. For example, for a factor of two differencebetween the downlink and uplink data rates, a 4/3 factor increase indata transport can be achieved. The larger the asymmetry between thedownlink and uplink data rates, the larger will be the increase in datatransport using the unidirectional channel transport mechanism aroundthe ring.

Referring again to FIG. 1, a further embodiment in accordance withanother aspect of the present invention may be better understood. In theevent that there is a significant change in asymmetry between thedownlink and uplink data rates and/or if there is a change in channelcomplement at the BTS, the Management Control module [discussed inconnection with FIG. 7 herein] which is typically comprised within eachDAU is able to automatically and adaptively re-allocate data transportresources on the clockwise direction of the ring and on thecounterclockwise direction of the ring to maximize the overall transportcapacity. As stated previously, the larger the degree of asymmetrybetween uplink and downlink data rates for a particular DAU, the higherthe increase in data transport using the unidirectional channeltransport mechanism around the ring. If there is more than one DAUpresent, in an embodiment one DAU is designated a Master DAU by the NOC,and the Management Control module located in the Master DAU makesdecisions to optimize the overall transport capacity. In the event themaster DAU fails, the NOC can designate another DAU as master.Alternatively, any suitable failover algorithm can be implemented.

Referring to FIG. 3, an alternative embodiment of the present inventionwherein a single DAU controls a plurality of rings, each comprising aplurality of daisy-chained DRU's, can be better understood. In FIG. 3,two daisy-chained rings, indicated at 300 and 305, are shown althoughthe number of rings could be greater and is determined mainly as amatter of design preference up to limits imposed by network performance.The rings each link a plurality of DRU's 310A-n and 315A-m, to a singleDAU 320. The directional flow of the data transport is shown as thedashed lines 325 and dotted lines 330. The downlink channels availablefrom the plurality of DRU's are divided into two subsets which flow inopposite directions around the two daisy-chained rings. The uplinkchannels are transported in a similar fashion. The channels are groupedinto the two subsets so as to maximize the data transport to and fromthe DRUs. The DAU in turn communicates with one or more BTS's via RFPorts 335A p.

Heuristic algorithms may be used to allocate RF channel data in aDual-ring DAS. For FIG. 3, there are two fibre rings R1, R2 (clockwiseand counter clockwise) and a set T of n≧2 independent RF channels Ki,1≦i≦n (including uplink and downlink). A channel Ki requires a bandwidthof b(Ki) to transport on a fibre ring. A time-bounded algorithm existswhich obtains a schedule having the optimal bandwidth allocation (i.e.the maximum aggregate bandwidth of each ring is as small as possible). Alarge number of advanced heuristic algorithms have been developed tosolve such scheduling optimization problems. Some examples are geneticalgorithm, evolutionary algorithm, greedy search, Tabu search, harmonysearch, simulated annealing, ant colony optimization, etc. For purposesof simplicity and clarity, a simple heuristic algorithm for two rings isdescribed here, although the number of rings is not limited to two.

The algorithm begins by sorting the channels Ki decreasingly bybandwidth b(Ki). Then it schedules the channel in such a way that eachchannel is assigned to the ring which has the smaller aggregatebandwidth. The formal description of the algorithm follows.

Input: T=set of n independent channels Ki with required bandwidth b(Ki),1≦i≦n.

Output: L₁, L₂ and D₁, D₂. Lj is the set of channels schedule on ringRj, and D_(j) is the maximum aggregate bandwidth of ring Rj,Dj=Dj=(Σb(J),JεL_(j)), 1≦j≦2.

ALGORITHM (T, L, D)

Step 1 (initialize Ki and D₁, D₂) Sort Ki such that b(Ki)≦b(Ki₊₁),1≦i≦n−1. D₁←0, D₂←0.

Step 2 (Schedule a channel)

For i=1 to n, step 1 do

If D₁≦D₂, then [assign Ki onto L₁, D₁←D₁+b(Ki)].

else [assign Ki onto L₂, D₂←D₂+b(Ki)].

Referring next to FIG. 4, a still further an alternative embodiment ofthe present invention may be understood. The arrangement illustrated inFIG. 1 comprised downlink signals from two separate base stationsbelonging to the same wireless operator entering the DAU 105 at inputports 110A and 110 p, respectively. In the embodiment of FIG. 4, a firstcomposite signal enters a first DAU 400 at that DAU's RF input port froma base station 405, and a second composite downlink input signal from,e.g., a second base station 410 belonging to a different wirelessoperator enters DAU 415 at that second DAU's RF input port. DAU 400directly supports two rings 420 and 425, DAU 415 directly supports tworings 430 and 435, and a ring 440 is shared between DAU 400 and DAU 405.Each of the rings comprises daisy-chained DRU's generally indicated at445 and connected via, for example, fiber optic links, as discussed inconnection with FIG. 1. It will be noted that channels A are transportedin the opposite sense as channels B. The downlink channels in subset Aare transported counterclockwise around each ring, whereas the channelsin subset B are transported in a clockwise sense around each ring. Inthis embodiment, signals belonging to both the first operator and thesecond operator are converted and transported to the DRU's 445 on ring440 because DAU 400 and DAU 405 are daisy-chained through the fiberoptic cable 440. This embodiment provides an example of a neutral hostwireless system, where multiple wireless operators share a commoninfrastructure comprised of DAU 400, DAU 415, and DRU's 445. All thepreviously mentioned features and advantages accrue to each of the twowireless operators. It will further be appreciated that, while FIG. 4illustrates only two DAU's linked in daisy-chain style, it is possibleto daisy chain a larger plurality of DAU's, and the daisy-chained DAU'scan also be configured in a ring configuration similar to the manner inwhich the DRU's are connected. This arranged is illustrated in FIG. 8,below.

As disclosed in U.S. Provisional Application Ser. No. 61/374,593,entitled “Neutral Host Architecture for a Distributed Antenna System,”filed Aug. 17, 2010 and again referring to FIG. 1 of the instant patentapplication, the Digital Up Converters present in the DRU's of thepresent invention can be programmed to process various signal formatsand modulation types including FDMA, CDMA, TDMA, OFDMA and others. Also,the Digital Up Converters present in the respective DRUs can beprogrammed to operate with signals to be transmitted within variousfrequency bands subject to the capabilities and limitations of thesystem architecture disclosed in U.S. Provisional Application Ser. No.61/374,593, mentioned above. In one embodiment of the present inventionwhere a wideband CDMA signal is present within, e.g., the bandwidthcorresponding to a first carrier at the input port to DAU 105, thetransmitted signal at the antenna ports of DRU 125A, DRU 1256 and DRUkwill be a wideband CDMA signal which is virtually identical to thesignal present within the bandwidth corresponding to that first carrierat the input port to DAU 105.

As disclosed in U.S. Provisional Application Ser. No. 61/374,593, againidentified above, and also referring to FIG. 1 of the instant patentapplication, it is to be understood that the Digital Up Converterspresent in the respective DRUs can be programmed to transmit any desiredcomposite signal format to each of the respective DRU antenna ports. Asan example, the Digital Up Converters present in DRU 125A and DRU 125Bcan be dynamically software-reconfigured as described previously so thatthe signal present at the antenna port of DRU 125A would correspond tothe spectral profile shown in FIG. 1 as 155A and also that the signalpresent at the antenna port of DRU 125B would correspond to the spectralprofile shown in FIG. 1 as 155B. The application for such a dynamicre-arrangement of DRU capacity would be e.g., if a company meeting weresuddenly convened in the area of the enterprise corresponding to thecoverage area of DRU 125B.

Referring again to FIG. 2, another embodiment of the Distributed AntennaSystem of the present invention can be better understood. As disclosedin the aforementioned U.S. Provisional Application Ser. No. 61/374,593,and also as shown in FIG. 2, the optical ring transport mechanism can beimplemented with regard to uplink signals. As discussed previously withregard to downlink signals and by referring to FIG. 1, the uplink systemshown in FIG. 2 is mainly comprised of DAU 105, together with DRU's125A-125 k. In a manner similar to the downlink operation explained byreferring to FIG. 1, the operation of the uplink system shown in FIG. 2can be understood as follows.

The Digital Down Converters present in each of DRU's 125A-k aredynamically software-configured as described previously so that uplinksignals of the appropriate desired signal format(s) present at thereceive antenna ports of the respective DRU's 125A-125 k are selectedbased on the desired uplink band(s) to be processed and filtered,converted and transported to the appropriate uplink output port of DAU105. The DAU and DRUs frame the individual data packets corresponding totheir respective radio signature using the Common Public InterfaceStandard (CPRI). Other Interface standards are applicable provided theyuniquely identify data packets with respective DRUs. Header informationis transmitted along with the data packet which indentifies the DRU andDAU that corresponds to the individual data packet.

In one example for the embodiment shown in FIG. 2, DRU's 125A and 125Care configured to receive uplink signals within the Channel K bandwidth,whereas DRU 1256 and DRU 125 n are both configured to reject uplinksignals within the Channel K bandwidth. When DRU 125C receives a strongenough signal at its receive antenna port within the Channel K bandwidthto be properly filtered and processed, the Digital Down Converterswithin DRU 125C facilitate processing and conversion. Similarly, whenDRU 125A receives a strong enough signal at its receive antenna portwithin the Channel K bandwidth to be properly filtered and processed,the Digital Down Converters within DRU 125A facilitate processing andconversion. The signals from DRU 125A and DRU 125C are combined based onthe active signal combining algorithm, and are fed to the base stationconnected to the uplink output port of DAU 105. The term simulcast isfrequently used to describe the operation of DRU 125A and DRU 125C withregard to uplink and downlink signals within Channel K bandwidth. Theterm Flexible Simulcast refers to the fact that the present inventionsupports dynamic and/or manual rearrangement of which specific DRU areinvolved in the signal combining process for each Channel bandwidth.

Referring still to FIG. 2, the Digital Down Converters present in DRU125A are configured to receive and process signals within Channel J-Qbandwidths. The Digital Down Converters present in DRU 1256 areconfigured to receive and process signals within Channel J, L, M and Obandwidths. The Digital Down Converters present in DRU 125C areconfigured to receive and process signals within Channel K and Obandwidths. The Digital Down Converters present in DRU 125 n areconfigured to receive and process signals within Channel J, M, N and Qbandwidths. The respective high-speed digital signals resulting fromprocessing performed within each of the four DRU are routed to the DAU.As described previously, the uplink signals from the four DRUs arecombined within the respective DAU corresponding to each base station.

In summary, the Reconfigurable Distributed Antenna System of the presentinvention described herein efficiently conserves resources and reducescosts. The reconfigurable system is adaptive or manuallyfield-programmable, since the algorithms can be adjusted like softwarein the digital processor at any time.

Referring next to FIG. 5, an alternative embodiment of the presentinvention may be better understood. FIG. 5 provides a daisy chainexample of a distributed antenna system (DAS). Each DRU has a coverageradius that can be adjusted based on the power transmission from thatparticular remote unit. The DAU controls the various DRU's transmissionpower and can optimize the overall coverage zone. In the illustratedembodiment, DAU 502, again under the control of a NOC (not shown), isassociated with a base station 501 and in turn interfaces with threeDRU's 503, 504 and 505. A user 506 with a mobile device is providedrelatively uniform coverage throughout the area covered by the threeDRU's.

Referring next to FIG. 6, a still further alternative embodiment may bebetter appreciated. FIG. 6 shows an embodiment of a multi-band systemillustrating one DAU supporting up to six different services operatingat different frequency bands, with three optical rings of DRU's 1-60.The input frequency bands 605-630 (here denoted as six frequency bandsat 700, 800, 850, 1900, 2100 and 2600 MHz) are input into the DAU 600from the BTS's (not shown). The DAU includes, among otherfunctionalities discussed herein, an RF IN portion for each band, and adigital distribution matrix for distributing the frequency bands to aplurality of DRU's, indicated as DRU1-DRU60, daisy-chained along threeseparate rings 635, 640 and 645 for achieving the desired coverage. Thefrequency bands are transported to either all or a subset of DRUs. Theparticular number of frequency bands, DAU's, DRU's and rings isexemplary only, and can, in practice, be any number appropriate to theperformance capabilities and needs of the network.

Referring next to FIG. 7 that illustrates embedded software controlmodules, the software embedded in the DAU and DRU, which controls theoperation of key functions of these devices, can be better understood.In particular, the DAU embedded software control module 700 comprises aDAU Management Control Module 705 and a DAU monitoring module 710. TheDAU Management Control Module 705 communicates with the NOC 715, andalso the DAU monitoring module 710. One such key function is determiningand/or setting the appropriate amount of radio resources (such as RFcarriers, CDMA codes or TDMA time slots) assigned to a particular DRU orgroup of DRUs to meet desired capacity and throughput objectives. Asnoted previously, the NOC 715 monitors the DAS operation and sendscommands to the DAU's for configuring various functions of the DRU's aswell as the DAU, in at least some embodiments.

The DAU Monitoring module, in addition to other functions, detects whichcarriers and corresponding time slots are active for each DRU. The DAUManagement Control module communicates with the DRU Embedded SoftwareControl module 720 over a fiber optic link control channel via a controlprotocol. In an embodiment, the control protocol comprises headerstogether with packets of data, such that both control information anddata are transmitted to the DRU's together as a message. DRU functionsor features that the header would control in the DRU are typicallyimplementation specific and can include, among other things, measuringuplink and downlink power, measuring gain of uplink and downlink, andmonitoring alarms in the DRU.

In turn, the DRU Management Control module 725 within the DRU EmbeddedSoftware Control Module sets the individual parameters of all the DRUDigital Up-Converters 730 to enable or disable specific radio resourcesfrom being transmitted by a particular DRU or group of DRUs, and alsosets the individual parameters of all the DRU Digital Down-Converters735 to enable or disable specific radio resources from being transmittedby a particular DRU or group of DRUs. In addition, the DRU EmbeddedSoftware Control Module comprises a DRU Pilot Beacon Control Module 740,which communicates with a DRU Pilot Beacon 745.

Referring next to FIG. 8, an embodiment of a daisy-chained configurationof DAU's is illustrated, together with a daisy-chained configuration ofDRU's. In an embodiment, a plurality of base stations 800A-800 n areeach associated with one of DAU's 805A-n. The DAU's are daisy-chained,and each DAU communicates with one or more daisy-chains 810A-810 m ofDRU's which may or may not be arranged in a ring configuration. It willbe appreciated that the DAU's can also be configured in a ringconfiguration, as discussed above.

An algorithm operating within the DAU Monitoring module which detectswhich carriers and corresponding time slots for each carrier are activefor each DRU provides information to the DAU Management Control moduleto help identify when, e.g., a particular downlink carrier is loaded bya percentage greater than a predetermined threshold whose value iscommunicated to the DAU Management Control module by the DAU's RemoteMonitoring and Control function 715. If that occurs, the DAU ManagementControl module can adaptively modify the system configuration to beginto deploy, typically although not necessarily slowly, additional radioresources (such as RF carriers, CDMA codes or TDMA time slots) for useby a particular DRU which need those radio resources within its coveragearea. At the same time, usually the DAU Management Control moduleadaptively modifies the system configuration to begin to remove, againtypically slowly, certain radio resources (such as RF carriers, CDMAcodes or TDMA time slots) for use by a particular DRU where that DRU nolonger needs those radio resources within its coverage area.

Although the present invention has been described with reference to thepreferred embodiments, it will be understood that the invention is notlimited to the details described thereof. Various substitutions andmodifications have been suggested in the foregoing description, andothers will occur to those of ordinary skill in the art. Therefore, allsuch substitutions and modifications are intended to be embraced withinthe scope of the invention as defined in the appended claims.

APPENDIX I Glossary of Terms

-   ACLR Adjacent Channel Leakage Ratio-   ACPR Adjacent Channel Power Ratio-   ADC Analog to Digital Converter-   AQDM Analog Quadrature Demodulator-   AQM Analog Quadrature Modulator-   AQDMC Analog Quadrature Demodulator Corrector-   AQMC Analog Quadrature Modulator Corrector-   BPF Bandpass Filter-   BTS Base Transceiver System or Base Station-   CDMA Code Division Multiple Access-   CFR Crest Factor Reduction-   DAC Digital to Analog Converter-   DAU Digital Access Unit-   DET Detector-   DHMPA Digital Hybrid Mode Power Amplifier-   DDC Digital Down Converter-   DNC Down Converter-   DPA Doherty Power Amplifier-   DQDM Digital Quadrature Demodulator-   DQM Digital Quadrature Modulator-   DSP Digital Signal Processing-   DUC Digital Up Converter-   EER Envelope Elimination and Restoration-   EF Envelope Following-   ET Envelope Tracking-   EVM Error Vector Magnitude-   FFLPA Feedforward Linear Power Amplifier-   FIR Finite Impulse Response-   FPGA Field-Programmable Gate Array-   GSM Global System for Mobile communications-   I-Q In-phase/Quadrature-   IF Intermediate Frequency-   LINC Linear Amplification using Nonlinear Components-   LO Local Oscillator-   LPF Low Pass Filter-   MCPA Multi-Carrier Power Amplifier-   MDS Multi-Directional Search-   OFDM Orthogonal Frequency Division Multiplexing-   PA Power Amplifier-   PAPR Peak-to-Average Power Ratio-   PD Digital Baseband Predistortion-   PLL Phase Locked Loop-   PN Pseudo-Noise-   QAM Quadrature Amplitude Modulation-   QPSK Quadrature Phase Shift Keying-   RF Radio Frequency-   RRH Remote Radio Head-   RRU Remote Radio Head Unit-   SAW Surface Acoustic Wave Filter-   UMTS Universal Mobile Telecommunications System-   UPC Up Converter-   WCDMA Wideband Code Division Multiple Access-   WLAN Wireless Local Area Network

What is claimed is:
 1. A method of communicating in a distributedantenna system (DAS), the method comprising: providing a plurality ofdigital remote units; providing at least one digital access unitconfigured to communicate with the plurality of digital remote units,wherein the plurality of digital remote units and the at least onedigital access unit are daisy-chained such that each digital remote unitis coupled to a next digital remote unit or to the at least one digitalaccess unit, the at least one digital access unit configured to receivea plurality of downlink channels from at least one signal source and tosend the plurality of downlink channels to the plurality of digitalremote units; sending a first portion of the plurality of downlinkchannels from the at least one digital access unit to a first digitalremote unit of the plurality of digital remote units; and sending asecond portion of the plurality of downlink channels from the at leastone digital access unit to a second digital remote unit of the pluralityof digital remote units, wherein a number of channels in the firstportion of the plurality of downlink channels is different from a numberof channels in the second portion of the plurality of downlink channels,and at least some channels in the first portion of the plurality ofdownlink channels are same as some channels in the second portion of theplurality of downlink channels and at least some channels in the firstportion of the plurality of downlink channels are different from somechannels in the second portion of the plurality of downlink channels. 2.The method of claim 1 wherein the first digital remote unit isconfigured to transmit the first portion of the plurality of downlinkchannels received from the at least one digital access unit and toreceive a corresponding first portion of uplink channels.
 3. The methodof claim 1 wherein the second digital remote unit is configured totransmit the second portion of the plurality of downlink channelsreceived from the at least one digital access unit and to receive acorresponding second portion of uplink channels.
 4. The method of claim1 wherein the plurality of digital remote units and the at least onedigital access unit are daisy-chained in a ring and each digital remoteunit is accessible by the at least one digital access unit in eitherdirection around the ring.
 5. The method of claim 1 wherein the at leastone digital access unit comprises a plurality of digital access unitseach coupled to at least one of the plurality of digital access units.6. The method of claim 1 wherein a number of the first portion of theplurality of downlink channels is less than a number of the secondportion of the plurality of downlink channels.
 7. The method of claim 1wherein the plurality of downlink channels comprise a plurality ofcarriers.
 8. The method of claim 1 wherein the plurality of downlinkchannels comprise a plurality of frequency bands.
 9. A method ofcommunicating in a distributed antenna system (DAS), the methodcomprising: providing a plurality of digital remote units; providing aplurality of digital access units, at least one of the plurality ofdigital access units configured to communicate with the plurality ofdigital remote units, wherein the plurality of digital remote units andthe plurality of digital access units are daisy-chained such that eachdigital remote unit is coupled to a next digital remote unit or to adigital access unit, the at least one of the plurality of digital accessunits configured to receive a plurality of downlink channels from atleast one signal source and to send the plurality of downlink channelsto the plurality of digital remote units; sending a first portion of theplurality of downlink channels from the at least one of the plurality ofdigital access units to a first digital remote unit of the plurality ofdigital remote units; and sending a second portion of the plurality ofdownlink channels from the at least one of the plurality of digitalaccess units to a second digital remote unit of the plurality of digitalremote units, wherein a number of channels in the first portion of theplurality of downlink channels is different from a number of channels inthe second portion of the plurality of downlink channels, and at leastsome channels in the first portion of the plurality of downlink channelsare same as some channels in the second portion of the plurality ofdownlink channels, and at least some channels in the first portion ofthe plurality of downlink channels are different from some channels inthe second portion of the plurality of downlink channels.
 10. The methodof claim 9 wherein the first digital remote unit is configured totransmit the first portion of the plurality of downlink channelsreceived from the at least one of the plurality of digital access unitsand to receive a corresponding first portion of uplink channels.
 11. Themethod of claim 9 wherein the second digital remote unit is configuredto transmit the second portion of the plurality of downlink channelsreceived from the at least one of the plurality of digital access unitsand to receive a corresponding second portion of uplink channels. 12.The method of claim 9 wherein the plurality of digital remote units andthe at least one of the plurality of digital access units aredaisy-chained in a ring and each digital remote unit is accessible bythe at least one of the plurality of digital access units in eitherdirection around the ring.
 13. The method of claim 9 wherein each of theplurality of digital access units are coupled to at least another one ofthe plurality of digital access units.
 14. The method of claim 9 whereina number of the first portion of the plurality of downlink channels isless than a number of the second portion of the plurality of downlinkchannels.
 15. The method of claim 9 wherein the plurality of downlinkchannels comprise a plurality of carriers.
 16. The method of claim 9wherein the plurality of downlink channels comprise a plurality offrequency bands.